The presence of foreign matters attaching to a rubber stopper for tight sealing, particularly a rubber stopper for medicament, such as for tight sealing a bottle for a medical injection liquid, is a recent, serious problem. The foreign matters include those which are retained on the rubber stopper even after washing, or those which are caused through contact of the rubber stopper with a medical liquid, and causes for their generation differ one from another. Specifically, when the surface of washed rubber stopper is observed by a scanning electron microscope at magnification of about 10.sup.2 -10.sup.3 times, the presence of indented locations or attachment of solid foreign matters can be observed thereon. It seems that they are connected to an increase in the number of foreign matters with time. A vulcanization accelerator, carbon black, zinc oxide, titanium oxide, sulfur, etc. are added to rubber, and it is inevitable to exude or elute these various additives or fillers to the surface of rubber stopper at the sterilization treatment of rubber stopper or at the contact with a medical liquid. Therefore, contamination of foreign matters cannot be eliminated by plugging an opening of a bottle for medical injection liquid with a rubber stopper and then conducting sterilization treatment thereof by hot water or steam, or by an ethylene oxide gas, while disregarding such a presence of foreign matters, though elimination of bacterial contamination can be attained. Thus, the essential solution of the problem has not been attained yet.
Furthermore, rubber material constituting the rubber stopper generally has a high coefficient of friction, which not only makes it more difficult to eliminate the bacteria or foreign matters from the surface of rubber stopper, but also makes rubber stoppers having readily adhesible surfaces readily adhesible to one another, and thus frequent generation of troubles is inevitable at the plugging operation. Chlorinated butyl rubber so far used as a rubber stopper material for vial bottles on account of excellence in gas impermeability, steam impermeability, anti-aging property, high and low temperature characteristics, etc. is a chlorination product of butyl rubber made by copolymerization of isobutylene as a major component with a small amount of isoprene, and thus a fear of occurrence of chemical reaction on the surface of rubber stopper is expected at the sterilization treatment by ethylene oxide gas.
To solve various problems encountered in such rubber stopper for tight sealing, particularly rubber stopper for medicament, such as for tight sealing a bottle for medical injection liquid, it has been proposed to coat the surface of rubber stopper with a film of specific synthetic resin or a vulcanized film of synthetic rubber. The film of synthetic resin can be formed by pasting a film of synthetic resin to an adhesive-coated surface of rubber stopper or integrally molding a film of synthetic resin on the surface part of rubber stopper, or the like, but these procedures are generally not only complicated in operation, but also are not applicable on account of shape of some rubber stopper. Furthermore, the film is often peeled off during the use on account of the insufficient adhesion strength. As the vulcanized film of synthetic rubber, a vulcanized film of fluorine rubber having a remarkable excellence in the chemical resistance and sliding characteristics can be contemplated, but the fluorine rubber itself has been so far used only as a parting agent, and thus its adhesiveness to various substrates including rubber is never satisfactory. For example, it is well known that the adhesiveness of vinylidene fluoride- hexafluoropropylene copolymer rubber, which is deemed to be typical fluorine rubber, to various substrates can be assured satisfactorily only by application of a primer or an adhesive.